The objective of this project is to investigate extracellular matrix-cell interactions employing an experimental system of matrix-induced endochondral bone differentiation. This experimental model further affords a method to undertake systematic studies on the biochemistry and physiology of endochondral bone formation. Subjects currently under investigation are: (1) transition in collagen and proteoglycan types during bone development; (2) changes in ornithine decarboxylase activity during bone cell differentiation; (3) hormonal and nutritional influences on bone formation; (4) influence of fluoride on the rate of mineralization; (5) role of magnesium in bone formation; and (6) matrix-cell interactions in tissue culture.